Understanding how Interleukin-5 blockade modulates both immune and metabolic pathways may clarify the multidimensional impact of biologic therapy in severe eosinophilic asthma. Therefore, this study aimed to assess the impact of mepolizumab on the nasal, bronchial, and systemic metabolomic profiles of consecutive patients with SEA and to explore the associations between these compartment-specific changes and clinical, inflammatory, and functional outcomes.

We conducted a prospective, observational, multicenter cohort study of SEA adult individuals initiating mepolizumab, with 12-month follow-up. Consecutive patients referred to the Pulmonary Rehabilitation Units of the Istituti Clinici Scientifici Maugeri IRCCS in Telese Terme and Tradate, Italy, from September 2021 to September 2023, were screened for eligibility based on the following inclusion criteria: eligibility for mepolizumab treatment according to clinical practice; age between 18 and 75 years; diagnosis of severe eosinophilic refractory asthma, defined as peripheral blood eosinophil count (BEC) > 300 cells/μL and at least two documented exacerbations within the previous 12 months; and ongoing treatment with high daily doses of inhaled corticosteroids (ICS) combined with long-acting β2-agonists (LABA), plus at least one additional controller medication for a minimum of 12 months.

Exclusion criteria included: current smoking; diagnosis of other chronic pulmonary diseases; coexisting chronic rhinosinusitis with nasal polyps; use of systemic corticosteroids at any dose within the 6 weeks prior to enrollment; use of immunosuppressive therapies; receipt of live attenuated vaccines within 30 days prior to enrollment; current or recent history (within the last 5 years) of malignancy, except in cases of complete remission; diagnosis of eosinophilic granulomatosis with polyangiitis (EGPA); upper or lower respiratory tract infections within 30 days prior to signing informed consent or during the screening/run-in period; any clinically significant abnormalities identified during screening through physical examination, vital signs assessment, hematology, or clinical chemistry, which, in the opinion of the investigator, could pose a risk to patient safety or interfere with study outcomes or compliance. Additional exclusion criteria were: known immunodeficiency (primary or secondary); pregnancy; concurrent treatment with other biologics for asthma or other conditions (except for stable allergen immunotherapy, defined as an unchanged dose and regimen at screening); prior biologic therapy for asthma within 6 months before starting mepolizumab; planned surgical procedures during the study period; and participation in another interventional or post-authorization safety study.

The study lasted 24 months, including a 12-month enrollment period followed by a 12-month follow-up. Timepoints at 6 and 12 months were prespecified to capture early consolidation of treatment response and its one-year persistence, in alignment with routine follow up. Prior to inclusion, all participants underwent a clinical examination to assess eligibility. Clinical history was recorded, including age at asthma onset, smoking status, aspirin intolerance, number of exacerbations in the previous year, and asthma control level. Smoking status was recorded as never, former, or current, and current smokers were excluded. Occupational and specific environmental exposures were not systematically collected in this study. Evaluations were performed at baseline (T0), 6 (T6), and 12 months (T12) after initiation of treatment. At each timepoint, respiratory function was assessed and multiple biological matrices were collected to test markers of T2 inflammation and enable metabolomic profiling.

Inclusion Criteria:

• Eligibility for mepolizumab treatment according to clinical practice;
• age between 18 and 75 years;
• diagnosis of severe eosinophilic refractory asthma, defined as peripheral blood eosinophil count (BEC) > 300 cells/μL and at least two documented exacerbations within the previous 12 months;
• ongoing treatment with high daily doses of inhaled corticosteroids (ICS) combined with long-acting β2-agonists (LABA), plus at least one additional controller medication for a minimum of 12 months.

Exclusion criteria:

• current smoking;
• diagnosis of other chronic pulmonary diseases;
• coexisting chronic rhinosinusitis with nasal polyps;
• use of systemic corticosteroids at any dose within the 6 weeks prior to enrollment;
• use of immunosuppressive therapies;
• receipt of live attenuated vaccines within 30 days prior to enrollment;
• current or recent history (within the last 5 years) of malignancy, except in cases of complete remission;
• diagnosis of eosinophilic granulomatosis with polyangiitis (EGPA);
• upper or lower respiratory tract infections within 30 days prior to signing informed consent or during the screening/run-in period;
• any clinically significant abnormalities identified during screening through physical examination, vital signs assessment, hematology, or clinical chemistry, which, in the opinion of the investigator, could pose a risk to patient safety or interfere with study outcomes or compliance.
• known immunodeficiency (primary or secondary);
• pregnancy;
• concurrent treatment with other biologics for asthma or other conditions (except for stable allergen immunotherapy, defined as an unchanged dose and regimen at screening); prior biologic therapy for asthma within 6 months before starting mepolizumab; planned surgical procedures during the study period;
• participation in another interventional or post-authorization safety study.

We will enroll patients with severe refractory eosinophilic asthma for whom treatment with mepolizumab is indicated, according to the AIFA recommendations.